The present disclosure relates to an image forming apparatus which forms an image on a sheet.
In an electrophotographic type image forming apparatus, when an abnormality such as a decreasing in density of a formed image and a scattering of a toner, is detected, countermeasures corresponding to the abnormality are taken. For example, a refresh operation in which a developer carried on a developer carrier is once discharged is carried out. Alternatively, a requirement for cleaning work by a service man is informed. Conventionally, such an abnormality is detected by an optical sensor detecting a scattered toner or a density of a formed image. For accurate detection, it is required to provide the optical sensor at a plurality of positions or to clean the optical sensor itself. This causes increasing in cost. Accordingly, it is desirable to detect such an abnormality without using the optical sensor as much as possible.
On the other hand, there is an image forming apparatus configured such that a toner consumption is calculated using an increasing degree of density of a toner image on an image carrier for a difference between a toner replenishment amount and a toner replenishment amount and then a toner replenishment amount is adjusted based on the calculated toner consumption.
In the image forming apparatus, the density of the toner imager on the image carrier is detected by a reflection type optical sensor. In this case, because a transferring rate of the toner to the image carrier is not 100% and the toner is overlapped on the image carrier, the toner consumption cannot be accurately detected using the density detected by the reflection type image sensor. In addition, if the image carrier such an intermediate transferring belt is damaged, an accurate density cannot be detected.